JP2015018923A - Optical semiconductor element and manufacturing apparatus of the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an optical semiconductor element having a larger optical gain and good optical characteristics with size equivalent with that of a conventional optical device.SOLUTION: An optical semiconductor element 20 comprises: a semiconductor substrate 21; a plurality of nanowire cores 25 which grow on the semiconductor substrate 21 an each of which includes a distortion semiconductor layer; and a semiconductor crystal layer 29 which forms one columnar structure 31 obtained by filling gaps among the plurality of nanowire cores 25 and which has the same crystal structure and the same plane direction with respect to an in-plane direction with those of the nanowire core 25. An optical distance between the neighboring nanowire cores 25 is smaller than an operating wavelength.

Description

  The present invention relates to an optical semiconductor element and a method for manufacturing the same.

  The use of semiconductor nanowires is expected as a means for realizing minute optical elements. In light-emitting elements such as lasers and LEDs, and light-receiving elements such as PIN photodiodes, the quantum well layer and quantum dot layer, which are generally functional layers, are generally multilayered from the viewpoint of gain and output, and the total volume of the active layer is increased. It is getting bigger. As a material for the quantum well or quantum dot, a strained semiconductor material having a lattice constant different from that of the base material is often used. Thereby, the quantum efficiency is increased by adjusting the operating wavelength, splitting the valence band degeneration, and the like. In particular, in the case of quantum dots, in order to form quantum dots by SK mode growth, a strain material having a large lattice mismatch amount of several percent is used.

  FIG. 1 is a configuration diagram of a general nanowire device. In the nanowire device 101 of FIG. 1A, an active layer 104 including a quantum well layer (or quantum dot layer) 102 is stacked in the radial direction (R direction) so as to surround the nanowire axis. In the nanowire device 111 of FIG. 1B, the active layer 114 is formed in a plane parallel to the substrate surface, and the quantum well (quantum dot) layer 112 is laminated in the axial direction or the height direction (H direction). . In either configuration, strain increases as the number of quantum well layers (quantum dot layers) 102 and 112 increases, so that there is a limit to the number of layers that can be stacked while maintaining crystallinity without causing dislocations. As a result, the obtained optical gain is limited.

  The first conductivity type Si substrate is etched to form a large number of nanowires, and a second conductivity type emitter layer is stacked on the nanowires to form a PN junction structure, and the PN junction structure is embedded with an ITO contact electrode. A solar cell has been proposed (see, for example, Patent Document 1). In addition, an optical element in which a structure in which each of a large number of Si nanowires is covered with a first conductive type semiconductor thin film is embedded with an intrinsic semiconductor (Si) and covered with a second conductive type semiconductor layer is known (for example, Patent Document 2).

Special table 2012-529756 gazette Special table 2011-527096 gazette

  Provided are an optical semiconductor element that realizes a larger optical gain and good optical characteristics with a size equivalent to that of a conventional optical device, and a method for manufacturing the same.

In one aspect, the optical semiconductor element is
A semiconductor substrate;
A plurality of nanowire cores grown on the semiconductor substrate, each having a strained semiconductor layer;
A semiconductor crystal layer that embeds between the plurality of nanowire cores to form one columnar structure, and has the same crystal structure and the same plane orientation as the nanowire core with respect to the in-plane direction of the semiconductor substrate Layers,
And the optical distance between the centers of the adjacent nanowire cores is smaller than the operating wavelength.

  An optical semiconductor element that achieves a larger optical gain and better optical characteristics with a size equivalent to that of a conventional optical device can be obtained.

It is the schematic which shows the general structural example of the nanowire containing the laminated | stacked active layer. It is the schematic which shows the structure of the optical semiconductor element of embodiment. It is a figure which shows the effect of the columnar structure containing the several nanowire core which laminated | stacked the quantum well layer in radial direction compared with the conventional structure. It is a figure which shows the effect of the columnar structure containing the several nanowire core which laminated | stacked the quantum well layer in the axial direction compared with the conventional structure. It is a figure which shows the change of the coupling coefficient of cores with respect to optical distance. 1 is a schematic configuration diagram of an optical semiconductor element of Example 1. FIG. FIG. 6 is a manufacturing process diagram of the optical semiconductor element of Example 1; FIG. 8 is a manufacturing process diagram of the optical semiconductor device of Example 1, showing the process following FIG. 7 (D). It is a manufacturing process figure of the optical semiconductor element of Example 1, and is a figure which shows the process following FIG.8 (D). 3 is a schematic configuration diagram of an optical semiconductor element of Example 2. FIG. 6 is a manufacturing process diagram of an optical semiconductor element of Example 2. FIG. FIG. 12 is a manufacturing process diagram for the optical semiconductor element of Example 2, showing the process following FIG. 11 (D). FIG. 13 is a manufacturing process diagram for the optical semiconductor element in Example 2, showing the process following FIG. 12 (D). It is a figure which shows the example of application of the optical semiconductor element of embodiment. It is a figure which shows the structural example in case the number of nanowire cores contained in a columnar structure is two pieces and four pieces. It is a figure explaining the total volume increase effect of an active layer when there are four nanowire cores.

  In the embodiment, two or more nanowire cores having a strained semiconductor layer such as a quantum well layer or a quantum dot layer are combined to form one columnar structure. At this time, the optical distance between the centers of adjacent nanowire cores is set to be shorter than the operating wavelength of the target. In the columnar structure, by dividing the strained semiconductor region into a plurality of layers, even if the number of strained semiconductor layers in each nanowire core is increased, the strain applied to one nanowire core can be kept within a range where crystallinity can be maintained. it can. Compared with a nanowire device having the same size as the columnar structure, the total volume of the strained semiconductor layer can be increased, so that the optical gain can be increased and the optical characteristics can be improved.

  FIG. 2 is a schematic diagram illustrating the configuration of the optical semiconductor element of the embodiment. The optical semiconductor element 1 in FIG. 2A has a columnar structure 5 having a height h on a semiconductor substrate 6. One columnar structure 5 includes a plurality of nanowire cores 3 and a semiconductor crystal layer 7 that groups the nanowire cores 3. Each nanowire core 3 has an active layer 4 including a strained semiconductor layer 2 stacked in the radial direction of the nanowire core 3. The strained semiconductor layer 2 is a quantum well layer, a quantum dot layer, or the like, and is, for example, the quantum well layer 2. The optical distance between the centers of adjacent nanowire cores 3 is shorter than the operating wavelength. The semiconductor crystal layer 7 is a layer having the same crystal structure and plane orientation as the nanowire core 3 in the in-plane direction of the substrate 6 (an epitaxial relationship is maintained).

  In the example of FIG. 2A, the columnar structure 5 includes three nanowire cores 3 having a height h. The cross-sectional shapes of the columnar structure 5 and the nanowire core 3 are both regular hexagons. Each of the plurality of nanowire cores 3 has a quantum well layer 2 stacked in the radial direction, and the total volume of the quantum well layers 2 included in one columnar structure 5 is a single unit having the same size as the columnar structure 5. It can be made larger than a single nanowire device.

  The optical semiconductor element 11 of FIG. 2B has a columnar structure 15 having a height h on a semiconductor substrate 16. One columnar structure 15 includes a plurality of nanowire cores 13 and a semiconductor crystal layer 17 that groups the nanowire cores 13. Each nanowire core 13 has an active layer 14 including a quantum well layer (strained semiconductor layer) 12 stacked in the axial direction or height h direction of the nanowire core 3. The optical distance between the centers of adjacent nanowire cores 13 is shorter than the operating wavelength. The semiconductor crystal layer 17 is a layer having the same crystal structure and plane orientation as the nanowire core 13 in the in-plane direction of the substrate 16 (an epitaxial relationship is maintained).

  In FIG. 2B, the columnar structure 15 includes three nanowire cores 13 having a height h. The cross-sectional shapes of the columnar structure 15 and the nanowire core 13 are both regular hexagons. Each of the plurality of nanowire cores 13 includes the quantum well layer 12 stacked in the axial direction, and the total volume of the strained semiconductor layer 12 included in one columnar structure 15 is a single unit having the same size as the columnar structure 15. It can be made larger than the nanowire device.

FIG. 3 is a diagram for explaining the effect of the optical semiconductor element 1 of FIG. The columnar structure 5 in FIG. 3A includes three nanowire cores 3, and each nanowire core 3 has a quantum well layer 2 stacked in the radial direction. The nanowire core 3 including the quantum well layer 2 has an outer diameter b ₂ and an inner diameter b ₁ .

As a comparative example, FIG. 3B shows a single nanowire device 101 having the same size and the same shape as the columnar structure 5. The nanowire device 101 including the quantum well layer 102 has an outer diameter a ₂ and an inner diameter a ₁ .

The heights of the nanowire core 3 and the nanowire device 101 are both h. The volume V _QW of the quantum well layer 102 of the nanowire device 101 in FIG. 3B is expressed by the formula (1).

On the other hand, the total volume V _TQW of the quantum well layer 2 having the configuration shown in FIG. 3A in which the quantum well region is divided into three is expressed by Expression (2).

  Considering the restriction that the device sizes are the same for fair comparison, the condition that the diameter of the columnar structure 5 including the three nanowire cores 3 is equal to or smaller than the diameter of the conventional nanowire device 101 (formula (3 )) Is imposed.

The difference ΔV _QW between the total volume of the quantum well layer 2 and the volume of the quantum well layer 102 is expressed by equation (4).

  In order for the total volume of the quantum well layer 2 of the columnar structure 5 to be larger than the total volume of the quantum well layer 102 of the nanowire device 101, the condition of formula (5) is derived.

  Expression (6) is established from Expression (4) and Expression (5).

  Moreover, since the film thickness of the quantum well layer 2 and the film thickness of the quantum well layer 102 are the same, Formula (7) is satisfy | filled.

  Expression (8) is derived from Expression (6) and Expression (7).

Considering the situation where the film thickness of the quantum well layer 2 is sufficiently thinner than the core diameter of the nanowire core 3, the lower limit of the inner diameter b ₁ of each nanowire core 3 (referred to as “divided core 3” as appropriate) is obtained from the equation (8). Equation (9) for determining is obtained.

Regarding the upper limit of the inner diameter b ₁ of the nanowire core 3, Equation (10) is obtained by considering the conditions for making the device size the same in a situation where the film thickness of the quantum well layer 2 is sufficiently thin.

Therefore, the range of the inner diameter b ₁ of the nanowire core 3 is determined by Expression (11).

The inner diameter b ₁ of the nanowire core 3 greater than a _1/3, by setting smaller than a _1/2, the same thickness as the quantum well layer 102 of the nanowire device 101 of the same size, the same number of layers and many more Volume can be obtained.

  In addition to this effect, if the diameter of each nanowire core 3 is reduced, it becomes stronger against strain, so that the effect that the number of quantum well layers 2 to be stacked can be increased is also obtained. The effect of increasing the number of stacked quantum well layers is also applicable when the quantum well layers are stacked in the axial direction, as will be described below.

  FIG. 4 is a diagram for explaining the effect of the optical semiconductor element 11 of FIG. The columnar structure 15 in FIG. 4A includes three nanowire cores 13, and each nanowire core 13 has a quantum well layer 12 stacked in the axial direction. Let the radius of each nanowire core 13 be b.

  As a comparative example, FIG. 4B shows a single nanowire device 111 having the same size and the same shape as the columnar structure 15. The radius of the nanowire device 111 is a.

When the number of stacked quantum well layers 112 of the nanowire device 113 is n, the total volume V _QW of the quantum well layers 112 is expressed by Expression (12).

When the number of stacked quantum well layers 12 in the columnar structure 15 in FIG. 4A is m, the total volume V _TQW of the quantum well layers 12 is expressed by Expression (13).

The ratio R _QW of the total volume V _TQW of the quantum well layer 12 to the total volume V _QW of the quantum well layer 112 is expressed by Expression (14).

When the ratio R _QW is greater than 1 (R _QW > 1), that is, b ² * m / a ² * n> 1, the total volume of the quantum well layers 12 distributed to the plurality of nanowire cores 13 is large. Become. In the nanowire device 111 of FIG. 4B, if the quantum well layer 112 has three layers, the nanowire core 13 is formed so that b = 0.45a, and five or more quantum well layers 12 are stacked. It is possible to fabricate the optical semiconductor element 11 having an increased gain while maintaining a favorable value.

  In order to uniformly inject carriers into a plurality of nanowire cores 3 (or 13) without loss, the semiconductor crystal layer 7 (which maintains an epitaxial relationship with the nanowire cores 3 (or 13) is formed between the cores. Or it is desirable to fill in 17).

In order to form the semiconductor crystal layer 7 so as to satisfy the epitaxial relationship with the nanowire core 3, a layer for masking crystal growth is provided on the bottom surface between the nanowire core 3 and the nanowire core 3, as will be described later. As the mask layer, SiO ₂ or SiN can be used. As a result, the semiconductor crystal layer 7 grows epitaxially in the radial direction (in-plane direction) of the nanowire core 3 and finally becomes an integrated single crystal layer. Since the nanowire core 3 and the semiconductor crystal layer 7 have the same crystal structure and plane orientation in the plane, a high-quality optical semiconductor element 1 with high carrier injection efficiency can be obtained. The same applies to the semiconductor crystal layer 17 in which the plurality of nanowire cores 13 are embedded.

  Further, when the positions of the center points of the adjacent three nanowire cores 3 form an equilateral triangle as shown in FIG. 3, the distance between the cores becomes a constant value. The nanowire cores 3 are simultaneously connected to each other by the growth in the horizontal direction 7 (the radial direction of the nanowire core 3). In this case, generation of voids at the interface between the nanowire core 3 and the semiconductor crystal layer 7 is suppressed, and a well-shaped columnar structure 5 can be obtained, thereby improving the carrier injection efficiency. The same applies to the optical semiconductor element 11 using the nanowire core 13 of FIG.

  In order to operate the columnar structure 5 (or 15) as a single optical device, the nanowire core 3 (or 13) is desirably disposed at a distance where the light modes of the cores are coupled.

  FIG. 5 shows the result of calculating the coupling coefficient change with respect to the normalized optical distance (optical distance / operating wavelength) of two adjacent nanowire cores. Here, the difference between the average refractive index of the nanowire core material and the refractive index of the semiconductor material filling between the cores is calculated as 0.1. If the optical distance between the cores is shorter than the wavelength (if the normalized optical distance is less than 1.0), 7% or more coupling is possible. In particular, when the normalized optical distance is 0.7 or less, 10% or more coupling is possible, and more stable operation is possible.

  From this simulation result, it is understood that the optical distance between the cores (refractive index × inter-core distance) is preferably equal to or shorter than the length of the operating wavelength, particularly 0.7 or shorter of the operating wavelength.

FIG. 6 shows a configuration example of the optical semiconductor element 20 of the first embodiment. The optical semiconductor element 20 has a configuration corresponding to the optical semiconductor element 1 of FIG. 2A and includes a columnar structure 31 including a plurality of nanowire cores 25. The nanowire core 25 is grown on the semiconductor substrate 21 using, for example, the SiO ₂ film 22 as a mask. An active layer 26 is laminated in the radial direction of each nanowire core 25. The nanowire core 25 is made of, for example, InP containing n-type impurities. The active layer 26 is formed by alternately laminating InAsP strain quantum well layers and InGaAsP barrier layers, for example.

  The nanowire core 25 covered with the active layer 26 is gathered by an intrinsic semiconductor crystal layer 27, and a semiconductor crystal layer 28 having a conductivity type opposite to that of the nanowire core is further provided around the nanowire core 25. In this example, the intrinsic semiconductor crystal layer 27 is an i-InP layer, and the semiconductor crystal layer 29 is an InP layer containing a p-type impurity. The InP nanowire core 25, the i-InP layer 27, and the p-type InP layer 28 have the same crystal structure and plane orientation and satisfy an epitaxial relationship in the in-plane direction.

  A transparent insulating film 35 is disposed on the upper surface of the columnar structure 31 and functions as a light extraction window. The upper electrode 34 formed on the SiN film 29 is connected to the p-type InP layer 28 on the side surface of the columnar structure 31. A bottom electrode 38 is formed on the back surface of the n-type InP substrate 21.

  7 to 9 are manufacturing process diagrams of the optical semiconductor element 20 of FIG.

In FIG. 7A, after depositing, for example, 50 nm of SiO _{2 serving} as a growth mask on an n-InP substrate 21 having a plane orientation of (111), an opening 23 is formed by lithography at a portion where the nanowire core is to be grown. Then, a metal thin film 24 serving as a growth catalyst is deposited. The diameter of the metal thin film 24 is preferably in the range of 10 to 100 nm. For example, gold (Au) is used as the metal material. The number of openings 23 per element is determined according to the purpose and application, but in this example, the three openings 23 are formed at the apex positions of equilateral triangles separated from each other by 200 nm.

In FIG. 7B, the n-InP nanowire core 25 is grown at a growth temperature of 300 to 500 ° C., for example, by the MOVPE method. Trimethyindium (TMIn) and phosphine (PH ₃ ) are used as raw materials. As an n-type impurity, for example, H ₂ S is supplied during growth to dope S. The S concentration is, for example, 1 × 10 ¹⁸ to 1 × 10 ²⁰ cm ⁻³ .

In FIG. 7C, the metal thin film 24 is removed by etching. Next, the active layer 26 is formed on the side surface of the nanowire core 25 again by the MOVPE method. As the active layer 26, InGaAsP barrier layers and InAsP strained quantum well layers are alternately stacked in the radial direction of the nanowire core 25 at a growth temperature of 500 to 600 ° C. (InGaAsP / InAsP active layer). Triethylgallium (TEGa) is used as the Ga raw material, and arsine (AsH ₃ ) is used as the As raw material. When the strain amount of InAsP is 1.5% and the film thickness is 2 nm, a quantum well having an operating wavelength in the 1.3 μm wavelength band can be formed. In this case, 1 to 3 InAsP quantum well layers are formed. The optical distance of the center distance of the nanowire core is approximately 200 × 3.2 = 640 nm, which is 49% of the operating wavelength, and thus the completed optical semiconductor element has a combination of light modes between the cores. It can operate as a single optical device.

In FIG. 7D, the i-InP layer 27 is grown at a growth temperature of 500 to 600.degree. By increasing the supply ratio (V / III ratio) of PH ₃ and TMIn to 2000 to 10,000 during growth, lateral growth (in-plane growth) can be maintained, and the nanowire core 25 can be appropriately connected. it can.

In FIG. 8A, a p-InP layer 28 is grown around the i-InP layer 27. Thereby, the columnar structure 31 is formed. When doping p-type impurities, for example, diethyl zinc (DEZn), which is a Zn raw material, is used. The Zn concentration is, for example, 5 × 10 ¹⁷ to 2 × 10 ¹⁸ cm ⁻³ . Although not shown, a p-InGaAs layer may be grown, for example, by 10 to 50 nm in order to form a low-resistance p-type electrode.

  In FIG. 8B, a SiN film 29 is formed on the entire surface by CVD. By CVD, the SiN film 29 on the side wall of the columnar structure 31 can be deposited so that the film thickness is smaller than the film thickness of the SiN film 29 on the surface parallel to the main surface of the substrate 21. The film thickness of the SiN film 29 on a plane parallel to the substrate 21 is 500 to 1500 nm.

  In FIG. 8C, a resist 32 is applied to the entire surface.

  In FIG. 8D, the resist 32 is processed to expose the SiN film 29 above the columnar structure 31.

  In FIG. 9A, the p-type InP layer 28 on the side wall of the columnar structure 31 is exposed by control etching while the SiN film 29 at the top of the columnar structure 31 is left. In this etching process, the thickness of the SiN film 29 on the upper surface of the columnar structure 31 is reduced, and the light extraction window 35 is formed. Thereafter, the resist 32 is removed.

  In FIG. 9B, a metal film 34 to be a p-electrode is formed by vapor deposition. As the metal film 34, for example, a multilayer film of Ti / Pt / Au may be used.

  In FIG. 9C, the portion of the metal film 34 to be left is protected with a resist 36.

  In FIG. 9D, the metal film 34 at the top of the columnar structure 31 is removed by dry etching to expose the light extraction window 35. An n-type metal electrode 38 is formed on the back surface of the SiN substrate 21 to obtain the surface emitting optical semiconductor element 20.

  FIG. 10 shows a configuration example of the optical semiconductor element 40 of the second embodiment. The optical semiconductor element 40 has a configuration corresponding to the optical semiconductor element 11 of FIG. 2B and includes a columnar structure 61 including a plurality of nanowire cores 50. An active layer 51 is laminated in the axial direction of each nanowire core 50. The active layer 51 is disposed between the first conductivity type semiconductor layer (for example, p-type AlGaAs layer) 45 and the second conductivity type semiconductor layer (for example, n-type AlGaAs layer) 52. The active layer 51 is formed by alternately laminating InGaAs strain quantum well layers and GaAs barrier layers, for example.

  The nanowire core 50 having the active layer 51 is combined with the semiconductor crystal layer 56 to form a columnar structure 61. In this example, the semiconductor crystal layer 56 is an i-GaAs layer. The semiconductor crystal layer 56 has the same crystal structure and the same plane orientation as the nanowire core 50 in the in-plane direction of the substrate 41 and maintains an epitaxial relationship. The side wall of the columnar structure 61 is covered with an insulating film 62. The exposed upper surface and part of the side wall of the columnar structure 61 are covered with a transparent conductive (ITO) film 65. An electrode film 68 is formed on the back surface of a semiconductor substrate (for example, a p-type GaAs substrate) 41.

  11 to 13 are manufacturing process diagrams of the optical semiconductor element 40 of FIG.

In FIG. 11A, after depositing, for example, 50 nm of a SiO ₂ layer 42 as a growth mask on a p-type GaAs substrate 41 having a plane orientation of (111), an opening 43 is formed at a predetermined location to grow nanowires. A metal thin film 44 serving as a catalyst is deposited. The diameter of the metal thin film 44 is preferably in the range of 10 to 100 nm. For example, gold (Au) is used as the metal material.

In FIG. 11B, the nanowire core layer 45 of the first conductivity type is formed by, for example, the MOVPE method. In this example, the p-type AlGaAs core layer 45 is grown at a growth temperature of 300 to 500 ° C. Trimethylaluminum (TMAl), triethylgallium (TEGa), and arsine (AsH ₃ ) are used as source gases. For example, DEZn is used for p-type doping. The Zn concentration is 1 × 10 ¹⁹ to 1 × 10 ²⁰ cm ⁻³ .

In FIG. 11C, an active layer 51 is grown on the p-type core layer 45. When the GaAs barrier layer 47 and the InGaAs strained quantum well layer 48 are formed as the active layer 51, the growth temperature is 300 to 500 ° C., and trimethylaluminum (TMAl), triethylgallium (TEGa), trimethylindium (TMIn), arsine (AsH ₃ ) Control the supply.

In FIG. 11D, a second conductivity type nanowire core layer 52 is formed on the active layer 51 by MOVPE. In this example, the n-type AlGaAs layer 52 is grown at a growth temperature of 300 to 500 ° C. Trimethylaluminum (TMAl), triethylgallium (TEGa), and arsine (AsH ₃ ) are used as source gases. H ₂ S is used for n-type doping. The S concentration is, for example, 1 × 10 ¹⁸ to 1 × 10 ¹⁹ cm ⁻³ .

In FIG. 12A, the metal thin film 44 is removed by etching. As a result, a plurality of nanowire cores 50 remain on the semiconductor substrate 41 masked by the SiO ₂ layer 42.

In FIG. 12B, a plurality of nanowire cores 50 are combined with an intrinsic semiconductor layer 56 to form a columnar structure 61. As the intrinsic semiconductor layer 56, for example, the i-GaAs layer 56 is grown at a growth temperature of 500 to 600 ° C. During growth, in particular, by increasing the supply ratio (V / III ratio) of AsH ₃ and TEGa to 1000 to 5000, the lateral growth (in-plane direction) is maintained, and the nanowire core 50 is appropriately connected. Can do.

In FIG. 12C, a SiO ₂ film 62 is formed on the entire surface by CVD. The thickness of the SiO ₂ film 62 is 500 to 1500 nm at the flat portion of the substrate surface and the upper surface of the columnar structure 61. The thickness of the SiO ₂ film 62 formed on the side wall of the columnar structure 61 is smaller than the thickness of the flat portion.

  In FIG. 12D, a resist 64 is applied and the upper surface of the columnar structure 61 and the i-GaAs layer 56 on the side wall are exposed by lithography and control etching.

  In FIG. 13A, the resist 64 is removed.

  In FIG. 13B, a transparent conductive film (ITO) 65 to be an n-type electrode is formed. Further, by forming the p-type metal electrode 68 on the back surface of the semiconductor substrate 41, the surface-emitting optical semiconductor element 40 is obtained.

  FIG. 14 shows an optical semiconductor element array 70 as an application example of the optical semiconductor element of the embodiment. For the optical semiconductor element array 70, the optical semiconductor element 20 (FIG. 6) of the first embodiment and the optical semiconductor element 40 (FIG. 10) of the second embodiment are applicable. In this example, the columnar structures 31 of the first embodiment are arranged in an array. Each columnar structure 31 includes three nanowire cores 25 having active layers 26 stacked in the radial direction.

A typical light emission cross-sectional area of the optical semiconductor element 20 of the first embodiment and the optical semiconductor element 40 of the second embodiment is on the order of μm ² , and light that can be detected by a normal near-infrared photodetector by itself. Output. Therefore, one optical semiconductor element 20 or 40 can be used as a single light source. By forming an appropriate reflective film on the upper surface of the columnar structure 31 or 61, the optical semiconductor element 20 or 40 can be used as a laser.

  Further, since the in-plane cross-sectional areas of the optical semiconductor elements 20 and 40 are small, they can be used for the optical semiconductor element array 70 as shown in FIG. When the optical semiconductor element array 70 is operated as a laser, it can be used as a light source of a multi-signal transmission device such as an optical interconnection. When operating as a light receiving element, it can be used as a high-definition image sensor by combining with a suitable microlens array.

  FIG. 15 is a diagram showing another example in which a plurality of nanowire cores are arranged. FIG. 15A shows a columnar structure 85 in which two nanowire cores 80 are arranged. Each nanowire core 80 has a strained semiconductor layer (for example, a quantum well layer) 82 stacked in the radial direction. FIG. 15B shows an example of a columnar structure 95 in which four nanowire cores 90 are arranged. Each nanowire core 90 has a strained semiconductor layer (for example, a quantum well layer) 92 stacked in the radial direction. The cross-sectional shape in the in-plane direction of the nanowire cores 80 and 90 is a quadrangle.

  The cross-sectional shape in the in-plane direction of the nanowire core can be controlled to be hexagonal or square by controlling the growth conditions of the semiconductor nanowire, and stable by selecting the plane orientation of the semiconductor substrate. Can grow into hexagons or squares. When a substrate having a plane orientation of (111) is used, nanowires having a hexagonal cross-sectional shape in the in-plane direction can be stably formed. When a substrate having a plane orientation of (100) is used, nanowires having a rectangular horizontal cross-sectional shape in the in-plane direction can be stably formed.

  FIG. 16 is a diagram for explaining the effect of increasing the total volume of the strained semiconductor layer when a plurality of nanowire cores are used. FIG. 16A shows an arrangement of quantum well layers 92 in a columnar structure 95 using four nanowire cores 90. As a comparative example, FIG. 16B shows an arrangement of quantum well layers 104 stacked on a single nanowire device 105 having the same size and the same shape as the columnar structure 95.

The volume V _QW of the quantum well layer 104 in FIG. 16B is expressed by Expression (15).

In contrast, in the configuration in which the active region of FIG. 16A is divided into four, the total volume V _TQW of the quantum well layer 92 is expressed by Expression (16).

  Here, for fair comparison, the constraint that the device sizes are the same, that is, the cross-sectional area in the in-plane direction of the columnar structure 95 including the four nanowire cores 90 is the surface of the single nanowire device 105. Imposes a condition that the cross sectional area is not more than the inward direction.

The volume difference ΔV _QW between the quantum well layer 92 of the columnar structure 96 and the quantum well layer 104 of the nanowire device 105 is expressed by Expression (18).

  In order for the volume of the quantum well layer 92 configured as shown in FIG. 16A to be larger than the volume of the quantum well layer 104 configured as shown in FIG. 16B, the condition of the equation (19) needs to be satisfied.

  Expression (20) is derived from Expression (18) and Expression (19).

  In the configurations of FIGS. 16A and 16B, the quantum well layer 104 and the quantum well layer 92 have the same film thickness, and therefore, the relationship of Expression (21) is established.

  Substituting equation (21) into equation (20) results in the relationship of equation (22).

Considering a situation in which the film thickness of the quantum well layers 92 and 104 is sufficiently thinner than the diameter of the nanowire core 90, the lower limit regarding the inner diameter b ₁ of the nanowire core 90 is given by Expression (23).

Further, by considering the conditions for making the device sizes the same in a situation where the quantum well layer 92 is sufficiently thin, the upper limit for the inner diameter b ₁ is given by equation (24).

From the expressions (23) and (24), the range of the inner diameter b ₁ is obtained.

  Comparing the columnar structure 95 and the nanowire device 105, even if the number of quantum well layers is the same, the columnar structure 95 obtained by dividing the quantum well region can further increase the volume of the quantum well.

  As described above, an optical semiconductor element in which the thickness of the active layer is sufficiently large can be manufactured using nanowires. Thereby, the gain of the optical semiconductor element can be increased and good optical characteristics can be realized.

  The above-described embodiment is an exemplification of the present invention, and includes other modifications. For example, when a nanowire core having a square cross-sectional shape in the in-plane direction is formed, a columnar structure having a rectangular (square or rectangular) cross-sectional shape by embedding an arbitrary number of nanowire cores with a semiconductor crystal layer that satisfies an epitaxial relationship The body can be formed.

The following notes are presented for the following explanation.
(Appendix 1)
A semiconductor substrate;
A plurality of nanowire cores grown on the semiconductor substrate, each having a strained semiconductor layer;
A semiconductor crystal layer that embeds between the plurality of nanowire cores to form one columnar structure, and has the same crystal structure and the same plane orientation as the nanowire core with respect to the in-plane direction of the semiconductor substrate Layers,
And an optical distance between the centers of the adjacent nanowire cores is smaller than an operating wavelength.
(Appendix 2)
On the semiconductor substrate, having a mask layer covering a region other than the nanowire core,
2. The optical semiconductor element according to appendix 1, wherein the semiconductor crystal layer is grown on the mask layer and connected to the nanowire core in the in-plane direction.
(Appendix 3)
Each of the nanowire cores includes an impurity of a first conductivity type,
The strained semiconductor layer is an undoped strained semiconductor layer laminated in the radial direction of the nanowire core on the sidewall of the nanowire core,
The semiconductor crystal layer includes an undoped first semiconductor crystal layer that groups the plurality of nanowire cores, and a second conductive layer that is disposed around the first semiconductor crystal layer and has the same crystal structure and the same plane orientation as the nanowire core. The optical semiconductor element according to appendix 1 or 2, further comprising a second semiconductor crystal layer of a type.
(Appendix 4)
Each nanowire core includes a first conductive type first core layer, a second conductive type second core layer, and the strained semiconductor layer positioned between the first core layer and the second core layer. An active layer,
The strained semiconductor layer is an undoped strained semiconductor layer laminated in the height direction of the nanowire core,
The optical semiconductor element according to appendix 1 or 2, wherein the semiconductor crystal layer is an undoped semiconductor crystal layer that groups the plurality of nanowire cores.
(Appendix 5)
The semiconductor substrate is a compound semiconductor substrate having a plane orientation of (111),
The optical semiconductor element according to any one of appendices 1 to 4, wherein a cross-sectional shape in the in-plane direction of the nanowire core and the columnar structure is a hexagon.
(Appendix 6)
The number of the nanowire cores included in the columnar structure is 3,
When the diameter of the nanowire core is b ₁ and the diameter of the columnar structure is a ₁ ,
_{(A 1/3) <b} 1 <(a 1/2)
The optical semiconductor element according to appendix 5, wherein the relationship is satisfied:
(Appendix 7)
The semiconductor substrate is a compound semiconductor substrate having a plane orientation of (100),
The optical semiconductor element according to any one of appendices 1 to 4, wherein a cross-sectional shape of the nanowire core and the columnar structure in the in-plane direction is a quadrangle.
(Appendix 8)
The number of the nanowire cores included in the columnar structure is 4,
The cross-sectional shape of the nanowire core and the columnar structure is a square,
When the diameter of the nanowire core is b ₁ and the diameter of the columnar structure is a ₁ ,
_{(A 1/4) <b} 1 <(a 1/2)
8. The optical semiconductor element according to appendix 7, wherein the relationship is satisfied.
(Appendix 9)
An optical semiconductor element array in which a plurality of the optical semiconductor elements according to any one of appendices 1 to 8 are arranged on the semiconductor substrate.
(Appendix 10)
On a semiconductor substrate, a plurality of nanowire cores each having a strained semiconductor layer are formed such that the optical distance between the centers of adjacent nanowire cores is shorter than the operating wavelength,
A space between the plurality of nanowire cores is embedded with a semiconductor crystal layer having the same crystal structure and the same plane orientation in the in-plane direction of the nanowire core and the semiconductor substrate to form a columnar structure.
The manufacturing method of the optical semiconductor element characterized by including a process.
(Appendix 11)
Forming a mask layer on the semiconductor substrate;
Forming an opening at a predetermined portion of the mask layer, and arranging the catalyst layer in the opening to grow the nanowire core;
The method for manufacturing an optical semiconductor element according to appendix 10, further comprising: growing the semiconductor crystal layer on the mask layer and connecting the semiconductor crystal layer to the nanowire core in the in-plane direction.
(Appendix 12)
Forming the nanowire core from a semiconductor material of a first conductivity type;
On the sidewall of the nanowire core, the undoped strained semiconductor layer is laminated in the radial direction of the nanowire core,
The columnar structure is formed by embedding a space between the plurality of nanowire cores on which the strained semiconductor layer is formed with an undoped first semiconductor crystal layer and surrounding the first semiconductor crystal layer with the same crystal as the nanowire core. 12. The method of manufacturing an optical semiconductor element according to appendix 10 or 11, comprising a step of forming a second conductive type second semiconductor crystal layer having a structure and the same plane orientation.
(Appendix 13)
The nanowire core is formed by forming a first conductive type first core layer on the semiconductor substrate, forming an undoped strained semiconductor layer on the first core layer, and forming the active layer. Forming a second core layer of the second conductivity type thereon,
12. The method for manufacturing an optical semiconductor element according to appendix 10 or 11, wherein a space between the nanowire cores on which the strained semiconductor layer is formed is embedded with the undoped semiconductor crystal layer.
(Appendix 14)
A compound semiconductor substrate having a (111) plane orientation is used as the semiconductor substrate,
14. The method of manufacturing an optical semiconductor element according to any one of appendices 10 to 13, wherein a cross-sectional shape in the in-plane direction of the nanowire core and the columnar structure is formed in a hexagon.
(Appendix 15)
A compound semiconductor substrate having a plane orientation of (100) is used as the semiconductor substrate,
14. The method for manufacturing an optical semiconductor element according to any one of appendices 10 to 13, wherein a cross-sectional shape in the in-plane direction of the nanowire core and the columnar structure is formed in a quadrangular shape.

1, 11, 20, 40 Optical semiconductor device 2, 12, 48, 82, 92 Quantum well layer (strained semiconductor layer)
3, 13, 25, 50, 69, 90 Nanowire core 4, 14, 26, 51 Active layer 5, 15, 31, 61, 85, 95 Columnar structure 6, 16, 21, 41 Semiconductor substrate 7, 17, 27 , 28, 56 Semiconductor crystal layers 22, 42 Mask layers 24, 44 Catalyst layer 70 Optical semiconductor element array

Claims (7)

A semiconductor substrate;
A plurality of nanowire cores grown on the semiconductor substrate, each having a strained semiconductor layer;
A semiconductor crystal layer that embeds between the plurality of nanowire cores to form one columnar structure, and has the same crystal structure and the same plane orientation as the nanowire core with respect to the in-plane direction of the semiconductor substrate Layers,
And an optical distance between the centers of the adjacent nanowire cores is smaller than an operating wavelength. On the semiconductor substrate, having a mask layer covering a region other than the nanowire core,
The optical semiconductor element according to claim 1, wherein the semiconductor crystal layer is grown on the mask layer and connected to the nanowire core in the in-plane direction. Each of the nanowire cores includes an impurity of a first conductivity type,
The strained semiconductor layer is an undoped strained semiconductor layer laminated in the radial direction of the nanowire core on the sidewall of the nanowire core,
The semiconductor crystal layer includes an undoped first semiconductor crystal layer that groups the plurality of nanowire cores, and a second conductive layer that is disposed around the first semiconductor crystal layer and has the same crystal structure and the same plane orientation as the nanowire core. The optical semiconductor element according to claim 1, further comprising a second semiconductor crystal layer of a type. Each nanowire core includes a first conductive type first core layer, a second conductive type second core layer, and the strained semiconductor layer positioned between the first core layer and the second core layer. An active layer,
The strained semiconductor layer is an undoped strained semiconductor layer laminated in the height direction of the nanowire core,
The optical semiconductor element according to claim 1, wherein the semiconductor crystal layer is an undoped semiconductor crystal layer that groups the plurality of nanowire cores.   An optical semiconductor element array in which a plurality of the optical semiconductor elements according to claim 1 are arranged on the semiconductor substrate. On a semiconductor substrate, a plurality of nanowire cores each having a strained semiconductor layer are formed such that the optical distance between the centers of adjacent nanowire cores is shorter than the operating wavelength,
A space between the plurality of nanowire cores is embedded with a semiconductor crystal layer having the same crystal structure and the same plane orientation in the in-plane direction of the nanowire core and the semiconductor substrate to form a columnar structure.
The manufacturing method of the optical semiconductor element characterized by including a process. Forming a mask layer on the semiconductor substrate;
Forming an opening at a predetermined portion of the mask layer, and arranging the catalyst layer in the opening to grow the nanowire core;
The method of manufacturing an optical semiconductor element according to claim 6, further comprising a step of growing the semiconductor crystal layer on the mask layer and connecting to the nanowire core in the in-plane direction.

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